The present invention relates to the art of power driven threading machines and, more particularly, to an improved base construction for such machines.
Power driven threading machines are of course well known and heretofore have included a one-piece cast aluminum base having opposite ends between which the various component parts of the machine are supported. More particularly in this respect, a spindle shaft is supported on the base by axially spaced apart bearing assemblies, and the shaft has an outer end which carries a centering chuck and an inner end which carries a chuck assembly by which a workpiece to be threaded is gripped and rotated. Tooling for cutting, reaming and threading a workpiece is supported on a carriage displaceable toward and away from the latter chuck along a pair of support rails. The cast base is basically a box-like structure having upright side walls and end walls and an intermediate wall between the end walls. The intermediate wall and one of the end walls provide cradles for the bearings supporting opposite ends of the spindle shaft, and the tooling carriage rails are supported between the intermediate wall and the other end wall of the base.
While threading machines having cast base constructions of the type described above are generally satisfactory in operation, the base casting has necessarily been large and heavy to accommodate the various component parts and, in particular, to enable the base to resist the torque and deflection forces imposed thereon during cutting, reaming and threading operations. The torque and deflection loads from such operations are applied primarily at the point of the front spindle shaft bearing and on the carriage support rails. It will be appreciated that the engagement between fixed tooling and a workpiece rotating about an axis offset from the carriage support rails and the side walls of the base produces a torque loading which tends to longitudinally twist the box-like base. A cast aluminum base having the required stiffness to resist such torsional loading, as well as deflection loading applied primarily between the front bearing and carriage support rails, weighs about 65 pounds in connection with a machine capable of threading workpieces up to 2 inches in diameter, and weighs well over 100 pounds in connection with a machine capable of threading workpieces between 21/2 inches and 4 inches in diameter. In addition to the undesirable size and weight characteristics, the amount of material required for the casting renders the base component undesirably expensive.